1. Field of the Invention
This invention relates to a process for preparing an emulsion of organopolysiloxane.
2. Description of the Prior Art
Known processes of preparing emulsions of liquid organopolysiloxane include a process of emulsifying liquid organopolysiloxane with use of an emulsifying agent by means of a stirring device that can exert a shearing force at high speed, for example, a homomixer, or ordinary stirring devices.
However, indispensable in the process in which the homomixer is used is that a liquid (the material to be emulsified) is sucked up through a hole provided in a stator and undergoes shearing action. In order for the liquid to be sucked up from the hole, the liquid is required to have at most a viscosity of about 10,000 cP or less. Thus, it has been impossible to emulsify organopolysiloxane of high viscosity, and yet impossible to prepare a good emulsion comprised of fine particles dispersed therein. Although it is possible to emulsify at least a fluid having a viscosity of about several ten thousands when the emulsification is carried out using an ordinary stirring device, the resulting emulsion may only have a particle size of as large as 10 to several tens microns in diameter. Since emulsion products are desired to be comprised of fine particles dispersed therein for the purpose of storage stability of emulsions and stability of dilution processing baths, those obtained by the above process can not be said to have satisfied such demands.
Also known in the present industrial field is a production process according to the so-called emulsion polymerization in which a low molecular cyclic organopolysiloxane used as a starting material is polymerized to a high molecular material with use of a strong acid or strong alkali as a catalyst in an emulsificaytion dispersion system (Japanese Patent Publication No. 13995/1966 and Japanese Patent Publication No. 20116/1969). This process has been widely put into practical use. According to this process, there can be relatively readily prepared even an emulsion of organopolysiloxane having a viscosity of more than 1,000,000 cP of the resulting polymeric product.
However, although the emulsion obtained by the emulsion polymerization can be made to have particle size of dispersed particles as small as about at least 0.2 micron and can have good stability, it involves substantial difficulties such that the emulsifying agents that can be used are limited to anionic or cationic ones and moreover about 10% of the starting organopolysiloxane may remain unpolymerized. The residual low molecular organopolysiloxane thus contained in the emulsion is volatilized when a resulting organopolysiloxane emulsion is used, accompanied by a fear of causing various difficulties such that oxidized white powder is formed by thermal oxidation during a drying step and adhered on the surface of surroundings to cause cissing of coating materials and further cause poor contact in contact points of electrical equipments present in the surroundings.